Olefin polymerization with pyridine moiety-containing singe-site catalysts

ABSTRACT

An olefin polymerization process is disclosed. The polymerization is performed in the presence of a clay, an activator, and a transition metal complex that has at least one pyridine moiety-containing ligand. The presence of clay increases the catalyst activity. The process is suitable for making ultra-high molecular weight polyethylenes (UHMWPE). The UHMWPE produced has increased bulk density.

FIELD OF THE INVENTION

The invention relates to olefin polymerization with pyridinemoiety-containing single-site catalysts. More particularly, theinvention relates to olefin polymerization with pyridinemoiety-containing single-site catalyst in the presence of clay.

BACKGROUND OF THE INVENTION

Pyridine based single-site catalysts are known. See U.S. Pat. No.5,637,660. These catalysts are particularly useful for making ultra-highmolecular weight polyethylene (UHMWPE). See U.S. Pat. No. 6,265,504.Unlike the conventional UHMWPE made with the Ziegler catalysts, thesingle-site UHMWPE has narrow molecular weight distribution. Thecatalysts, however, have relatively low activity and the UHMWPE producedhas relatively low bulk density.

Low catalyst activity means low efficiency and high cost of the polymerproduction. Similarly, low bulk density means low productivity perreactor unit. Polyethylene of low bulk density also dries slowly becauseit absorbs solvent and residual monomers. Further, low bulk density mayresult in inferior product quality.

New ethylene polymerization processes are needed. Ideally, the processwould use the readily available pyridine based single-site catalysts,give high catalyst activity, and produce UHMWPE having increased bulkdensity.

SUMMARY OF THE INVENTION

The invention is an olefin polymerization process. The process isperformed in the presence of a clay, an activator, and a transitionmetal complex having at least one pyridine moiety-containing ligand. Isurprisingly found that the use of clay in the process significantlyincreases the catalyst activity.

The invention also includes a process for preparing an ultra-highmolecular weight polyethylene (UHMWPE). The process comprisespolymerizing ethylene in the presence of a clay, a supported transitionmetal complex having at least one pyridine moiety-containing ligand, anda non-alumoxane activator. The process is performed in the absence ofaromatic solvent, α-olefin comonomer, and hydrogen. The process producesUHMWPE having an increased bulk density.

DETAILED DESCRIPTION OF THE INVENTION

The process of the invention comprises polymerizing an olefin in thepresence of a clay, an activator, and a transition metal complex havingat least one pyridine moiety-containing ligand.

Suitable olefins include C₂₋₂₀ α-olefins. Suitable olefins also includecyclic olefins and conjugated and non-conjugated dienes. Examples ofsuitable olefins are ethylene, propylene, 1-butene, 1-pentene, 1-hexene,1-octene, 4-methyl-1-pentene, butadiene, isoprene, cyclopentene,cyclohexene, norbornene, 1-methylnorbornene, 5-methylnorbornene, thelike, and mixtures thereof. Preferred olefins are C₂₋₁₀ α-olefins. Morepreferred olefins are ethylene, propylene, 1-butene, 1-pentene,1-hexene, and 1-octene. Most preferred olefins are ethylene and mixturesof ethylene with a C₃₋₁₀ α-olefin.

Suitable clays include montmorillonite, saponite, hectorite, mica,vermiculite, bentonite, nontronite, beidellite, volkonskoite, magadite,and kenyaite, the like, and mixtures thereof. Preferably, the clays aremodified, for example, with quaternary ammonium compounds. The modifiedclays are called organoclays. Organoclays are commercially available,for example, from Southern Clay Products, Inc., and Co-Op Chemical Co.,LTD.

Preferably, the clay is heat-treated prior to the use in thepolymerization. More preferably, the clay is heat-treated in thepolymerization reactor prior to the use in the polymerization. The heattreatment is preferably conducted at a temperature within the range of100° C. to 200° C.; more preferably from 125° C. to 165° C. The heattreatment removes moisture and other impurities from the clay.

Suitable activators include alumoxanes, alkyl aluminums, alkyl aluminumhalides, anionic compounds of boron or aluminum, trialkylboron andtriarylboron compounds. Examples include methyl alumoxane (MAO),polymeric MAO (PMAO), ethyl alumoxane, diisobutyl alumoxane,triethylaluminum, diethyl aluminum chloride, trimethylaluminum,triisobutyl aluminum, lithiumtetrakis(pentafluorophenyl) borate, lithiumtetrakis(pentafluoro-phenyl)aluminate, dimethylanilinium tetrakis(pentafluorophenyl)borate, trityl tetrakis (pentafluorophenyl)borate,tris(pentafluorophenyl)borane, triphenylborane, tri-n-octylborane, thelike, and mixtures thereof. MAO, PMAO, andtris-(pentafluorophenyl)borane are preferred.

Suitable transition metal complexes include those which have at leastone pyridine moiety-containing ligand. By “pyridine moiety-containingligand,” I mean any ligand that includes a pyridine ring structure.Preferably, the complex has the general structure:

M is a transition metal. Preferably, M is Group 4 transition metal. Morepreferably, M is Ti or Zr. Most preferably, M is Ti.

L₁ is a pyridine moiety-containing ligand. Preferably, L₁ has thegeneral structure:

Wherein Y is bonded to M and is selected from the group consisting of O,S, and NR wherein R is hydrogen or an alkyl group. One or more of theremaining ring atoms are optionally and independently substituted byalkyl, aryl, aralkyl, alkylaryl, silyl, halogen, alkoxy, aryloxy,siloxy, nitro, dialkyl amino, or diaryl amino groups and two adjacentsubstituents optionally form a ring structure.

L₂ is a ligand selected from the group consisting of L₁ ligands,cyclopentadienyls, indenyls, fluorenyls, boraaryls, azaborolinyls,indenoindolyls, and phosphinimines. Preferably, L₂ is selected from thegroup consisting of L₁ ligands and cyclopentadienyls. More preferably,L₂ is an L₁ ligand. Most preferably, L₂ is the same as L₁.

X is a ligand selected from the group consisting of halides, alkyl,aryl, alkoxy, aryloxy, dialkylamino, and siloxy groups. Preferably, X isselected from the group consisting of halides, aralkyl, and alkylarylgroups. More preferably, X is selected from chloride and benzyl. Eitherm or n can be zero; the sum of n and m satisfies the valence of M.

Example of suitable complexes are bis(2-pyridinoxy)ttanium dichloride,(cyclopentadienyl)(2-pyridinoxy)titanium dichloride, 8-quinolinoxytitanium trichlorde, 8-(2-methyl-5,7-dichloroquinolinoxy)titaniumtrichloride, bis(8-(2-methyl-5,7-dichloroquinolinoxy))titaniumdichloride, and 8-Quinolinoxytitanium tribenzyl.

Activators are generally used in an amount within the range of about0.01 to about 100,000, preferably from about 0.1 to about 1,000, andmost preferably from about 0.5 to about 50, moles per mole of thecomplex.

The complex is preferably supported. The support is preferably a porousmaterial such as inorganic oxides and chlorides, and organic polymerresins. Preferred inorganic oxides include oxides of Group 2, 3, 4, 5,13, or 14 elements. Preferred supports include silica, alumina,silica-aluminas, magnesias, titanias, zirconias, magnesium chloride, andcrosslinked polystyrene. Silica is most preferred.

Preferably, the support has a surface area in the range of about 10 toabout 900 m²/g, a pore volume in the range of about 0.1 to about 4.0mL/g, an average particle size in the range of about 10 to about 500 μm,and an average pore diameter in the range of about 10 to about 1000 Å.The support is preferably modified by heat treatment, chemicalmodification, or both. For heat treatment, the support is preferablyheated at a temperature from about 50° C. to about 800° C. Morepreferably, the temperature is from about 100° C. to about 400° C.

Suitable chemical modifiers include organoaluminum, organosilicon,organomagnesium, and organoboron compounds. Organosilicon andorganoboron compounds, such as hexamethyidisilazane (HMDS) andtriethylborane, are preferred. Suitable techniques for treating asupport are taught, for example, by U.S. Pat. No. 6,211,311, theteachings of which are incorporated herein by reference.

Preferably, the supporting involves treating a support withorganosilicon compounds, calcining the treated support, treating thecalcined support with organomagnesium compounds, mixing theorganomagnesium-treated support with a pyridine moiety-containingsingle-site complex, and then removing any solvents from the supportedcatalyst. More preferably, the supporting is performed by (1) treating asilica support with HMDS, (2) calcining the HMDS-treated silica (3)treating the calcined silica with dibutylmagnesium, (4) mixing thetreated silica of step 3 with a pyridine moiety-containing complex, and(5) removing any solvents. Example 1 shows a detailed procedure ofsupporting the catalyst.

Other suitable supporting techniques may be used. For example, thecatalyst may be supported by using the method taught by co-pending Appl.Ser. No. 09781,464. First, a quinolinol is deprotonated to produce ananionic ligand precursor. Second, the anionic ligand precursor reactswith about 0.5 equivalent of a transition metal compound to give amixture that contains quinolinoxy ligand-containing complex. Third, themixture reacts with a non-alumoxane activator. Fourth, the product fromstep three is combined with a support. Finally, the solvents are removedto give a solid, supported complex.

Optionally, the activator and the complex can be mixed and thensupported together. Alternatively, only the complex is supported.

The polymerization is preferably conducted at a temperature within therange of about 50° C. to 150° C., preferably about 75° C. to 135° C. Thepolymerization is preferably conducted under pressure. The reactorpressure is preferably within the range of about 100 to about 5,000 psi,more preferably from about 300 to about 3,000 psi, and most preferablyfrom about 500 to about 2,000 psi. Generally, the higher the pressure,the more productive the process.

The process of the invention includes solution, slurry and gas phasepolymerizations. In the solution or slurry process, aliphatic, cyclicand aromatic hydrocarbons are suitable solvents. Preferred solventsinclude pentane, hexane, heptane, octane, isobutane, cyclohexane,toluene, and the like, and mixtures thereof.

The invention includes a process for making an ultra-high molecularweight polyethylene (UHMWPE). The process uses a non-alumoxaneactivator. Suitable non-alumoxane activators for making UHMWPE includealkyl aluminums, alkyl aluminum halides, anionic compounds of boron oraluminum, trialkylboron and triarylboron compounds, and the like.Examples are triethylaluminum, trimethylaluminum, diethylaluminumchloride, lithium tetrakis(pentafluorophenyl) borate, triphenylcarbeniumtetrakis(pentafluorophenyl) borate, lithium tetrakis(pentafluorophenyl)aluminate, tris(pentafluorophenyl) boron, tris(pentabromophenyl) boron,and the like, and mixtures thereof.

The polymerization for making UHMWPE is preferably conducted at atemperature within the range of about 40° C. to 110° C., preferablyabout 50° C. to 80° C. A high polymerization temperature results in alow molecular weight of polyethylene. If the temperature is too high,UHMWPE cannot be obtained.

The polymerization for making UHMWPE is conducted in the absence of anaromatic solvent. Saturated aliphatic and cyclic hydrocarbons aresuitable solvents. Preferred solvents include pentane, hexane, heptane,octane, isobutane, cyclohexane, and the like, and mixtures thereof.Using an aromatic solvent in the process reduces the molecular weight ofpolyethylene. UHMWPE cannot be obtained when an aromatic solvent isused.

The polymerization for making UHMWPE is performed in the absence ofhydrogen or any other chain transfer agent. Using hydrogen in theprocess reduces the molecular weight of the polyethylene. UHMWPE cannotbe obtained in the presence of hydrogen.

The polymerization for making UHMWPE is conducted in the absence ofother a-olefin comonomers such as propylene, 1-butene, or 1-hexene.Incorporation of an α-olefin comonomer reduces the molecular weight ofpolyethylene. UHMWPE cannot be obtained when an α-olefin comonomer isused.

I have surprisingly found that the process of the invention gives muchhigher catalyst activity than the known process (see Table 1). Moresurprisingly, the process of the invention produces UHMWPE havingincreased bulk density.

UHMWPE made by the process of the invention has a weight averagemolecular weight (Mw) greater than about 3,000,000. Preferably, Mw isgreater than about 4,500,000. The UHMWPE has a bulk density greater than0.26 g/cc. Preferably, the UHMWPE has a bulk density is 0.3 g/cc orgreater.

The invention includes an UHMWPE. The UHMWPE contains a clay. Suitableclay includes those discussed above. Unlike other ethylene polymers,UHMWPE has poor thermal processability. Thus, it is difficult toincorporate clay into an UHMWPE by post polymerization process. Thisinvention provides a way to prepare an UHMWPE that contains clay. Theincorporated clay can improve the performance of the UHMWPE or functionas filler.

UHMWPE has a variety of uses. In particular, it can be advantageouslyused to make film, pressure pipe, large-part blow molding, extrudedsheet, and many other articles. It can be used alone or blended withother resins. Techniques for making these articles are well known in thepolyolefin industry.

The following examples merely illustrate the invention. Those skilled inthe art will recognize many variations that are within the spirit of theinvention and scope of the claims.

EXAMPLE 1 Polymerizing Ethylene with Supported 8-QuinolinoxytitaniumTribenzyl in the Presence of Clay

(A) Preparing 8-Quinolinoxytitanium Trichloride

Under nitrogen, 8quinolinol powder (1.45 g, 10.0 mmol) and heptane (100mL) are added to a flask and stirred. The stirring rate is adjusted toprevent solids from depositing on the walls of the flask. Titaniumtetrachloride (10 mL of 1.0 M solution in heptane) is added dropwise tothe flask over 20 hours at 25° C. at a stirring rate effective toprevent solids from depositing on the walls of the flask. The reactionmixture changes from white to tomato-juice red. The solids are isolatedby decanting the liquid portion. Residual solvent is removed from thesolids under vacuum, resulting in a red solid, which is8-quinolinoxytitanium trichloride (3.04 g).

(B) Preparing 8-Quinolinoxytitanium Tribenzyl

8-Quinolinoxytitanium trichloride (0.060 g, 0.2 mmol, prepared in (A) ismixed with toluene (10 mL). Benzylmagnesium chloride (0.60 mL of 1.0 Msolution in diethyl ether, 0.60 mmol) is added to the mixture withstirring at 25° C., resulting in a purple solution of8-quinolinoxytitanium tribenzyl (10 mL, 0.2 mmol).

(C) Supporting 8-Quinolinoxytitanium Tribenzyl

Silica (Davison 948, 5.0 g) is pretreated with HMDS and then calcined 4h at 600° C. The treated silica is suspended in heptane (25 mL).Dibutylmagnesium (5.0 mL of 10 wt % solution in heptane, 3.0 mmol) isadded to the silica suspension under nitrogen at 25° C.8-Quinolinoxytitanium tribenzyl (1.0 mmol) is dissolved indichloromethane (25 mL) to give a purple solution. This solution is thenadded to the above mixture at 25° C. under nitrogen over 1 h. Thesolvent is removed by nitrogen purge, and the catalyst is dried undervacuum for 0.5 h.

(D) Polymerization

Polymerization is conducted in a 2L stainless steel pressure reactor.

Lucentite™ organophilic clay (5 g, product of Co-Op Chemical Co., LTD)is added to the reactor. The reactor is heated at 150° C. for an hour,purged with nitrogen three times, and then sealed and cooled to 25° C.The supported quinolinoxytitanium tribenzyl (0.05 g), triethylaluminum(TEAL) (0.60 mL, 1.6 M in isobutane), and hexane (1,000 mL) are chargedinto the reactor. After the reactor contents are heated to 60° C.,ethylene, dried by passing through 13X molecular sieves, is fed into thereactor via a pressure regulator to start the polymerization. Thepolymerization is performed at 70° C. by continuously feeding ethyleneto maintain the reactor pressure at 550 psi. The polymerization isterminated by venting the reactor. Butylated hydroxytoluene (1,000 ppm)is added to the polymer. The polymer is dried for an hour at 80° C.under vacuum. It has Mw: 5.25×10⁶ g/mol. and bulk is density: 0.32 g/cc.The catalyst activity is 33,100 kg PE/mol cat/h.

EXAMPLE 2 Polymerizing Ethylene in the Presence of Clay

Example 1 is repeated, but in step (D), the clay is not heated at 150°C. for an hour. Rather, the empty reactor is heated at 130° C. for anhour, purged with nitrogen for 3 times, and then sealed and cooled to25° C. The clay (5 g), supported quinolinoxytitanium tribenzyl (0.05 g),triethylaluminum (TEAL) (0.60 mL, 1.6 M in isobutane), and hexane (1,000mL) are charged into the reactor. After the reactor contents are heatedto 60° C., ethylene, dried by passing through 13X molecular sieves, isfed into the reactor via a pressure regulator to start thepolymerization. The polymerization is performed at 70° C. bycontinuously feeding ethylene to maintain the reactor pressure at 550psi. The polymerization is terminated by venting the reactor. Butylatedhydroxytoluene (1,000 ppm) is added to the polymer. The polymer is driedfor an hour at 80° C. under vacuum. It has Mw: 5.14×10⁶ g/mol. and bulkdensity: 0.32 g/cc. The catalyst activity is 27,300 kg PE/mol cat/h.

EXAMPLE 3 Polymerizing Ethylene in the Presence of Clay

Example 1 is repeated, but in step (D), the clay is pre-heated at 150°C. for an hour outside of the reactor. The reactor is heated at 130° C.for an hour, purged with nitrogen three times, and then sealed andcooled to 25° C. The pre-heated clay (5 g), supportedquinolinoxytitanium tribenzyl (0.05 g), triethylaluminum (TEAL) (0.60mL, 1.6 M in isobutane), and hexane (1,000 mL) are charged into thereactor. After the reactor contents are heated to 60° C., ethylene,dried by passing through 13X molecular sieves, is fed into the reactorvia a pressure regulator to start the polymerization. The polymerizationis performed at 70° C. by continuously feeding ethylene to maintain thereactor pressure at 550 psi. The polymerization is terminated by ventingthe reactor. Butylated hydroxytoluene (1,000 ppm) is added to thepolymer. The polymer is dried for an hour at 80° C. under vacuum. It hasMw: 5.08×10⁶ g/mol. and bulk density: 0.31 g/cc. The catalyst activityis 16,000 kg PE/mol cat/h.

COMPARATIVE EXAMPLE 4 Polymerizing Ethylene in the Absence of Clay

Example 1 is repeated, but in step (D), no clay is added. The reactor isheated at 130° C. for an hour, purged with nitrogen three times, andthen sealed and cooled to 25° C. The supported quinolinoxytitaniumtribenzyl (0.05 g), triethylaluminum (TEAL) (0.60 mL, 1.6 M inisobutane), and hexane (1,000 mL) are charged into the reactor. Afterthe reactor contents are heated to 60° C., ethylene, dried by passingthrough 13X molecular sieves, is fed into the reactor via a pressureregulator to start the polymerization. The polymerization is performedat 70° C. by continuously feeding ethylene to maintain the reactorpressure at 550 psi. The polymerization is terminated by venting thereactor. Butylated hydroxytoluene (1,000 ppm) is added to the polymer.The polymer is dried for an hour at 80° C. under vacuum. It has Mw:4.04×10⁶ g/mol. and bulk density: 0.26 g/cc. The catalyst activity is9,600 kg PE/mol cat/h.

EXAMPLE 5 Polymerizing Ethylene in the Presence of Clay

Example 1 is repeated, but in step (D), isobutane rather than hexane isused as solvent and the reactor pressure remains at 300 psig rather than550 psig. The polyethylene has Mw: 4.97×10⁶ g/mol. and bulk density:0.31 g/cc. The catalyst activity is 10,000 kg PE/mol cat/h.

EXAMPLE 6 Polymerizing Ethylene in the Presence of Clay

Example 1 is repeated, but in step (D), the clay is pre-heated at 150°C. for an hour before added to the reactor. Isobutane rather than hexaneis used as solvent and the reactor pressure remains at 300 psig ratherthan 550 psig. The polyethylene has,Mw: 4.87×10⁶, g/mol. and bulkdensity: 0.30 g/cc. The catalyst activity is 9,000 kg PE/mol cat/h.

COMPARATIVE EXAMPLE 7 Polymerizing Ethylene in the Absence of Clay

Example 1 is repeated, but in step (D), no clay is added to the reactor.Isobutane rather than hexane is used as solvent and the reactor pressureremains at 300 psig rather than 550 psig. The polyethylene has Mw:3.99×10⁶ g/mol. and bulk density: 0.26 g/cc. The catalyst activity is7,800 kg PE/mol cat/h.

TABLE 1 Results Summary Catalyst Activity Polym. Ethylene Kg Bulk Ex.Temp. Pressure PE/mol Mw × Density No. Clay ° C. psig Solvent cat/h 10⁻6g/cc 1 yes 70 550 Hexane 33,100 5.25 0.32 2 yes 70 550 Hexane 27,3005.14 0.32 3 yes 70 550 Hexane 16,500 5.08 0.31 C4 no 70 550 Hexane 9,6004.04 0.26 5 yes 70 300 Iso- 10,000 4.97 0.31 butane 6 yes 70 300 Iso-9,000 4.87 0.30 butane C7 no 70 300 Iso- 7,800 3.99 0.26 butane

I claim:
 1. A process comprising polymerizing an olefin in the presenceof a clay, an activator, and a Group 4 transition metal complex havingat least one pyridine moiety-containing ligand.
 2. The process of claim1 wherein the transition metal complex has the general structure:

wherein M is a Group 4 transition metal; L₁ is a pyridinemoiety-containing ligand; L₂ is a ligand selected from the groupconsisting of L₁ ligands, cyclopentadienyls, indenyls, fluorenyls,boraaryls, azaborolinyls, indenoindolyls, and phosphinimines; X is aligand selected from the group consisting of alkyl, aryl, alkoxy,aryloxy, halide, dialkylamino, and siloxy groups; and the sum of n and msatisfies the valence of M.
 3. The process of claim 2 wherein the M isTi or Zr.
 4. The process of claim 2 wherein L₁ has the generalstructure:

wherein Y is bonded to M and is selected from the group consisting of O,S, and NR wherein R is hydrogen or an alkyl group; one or more of theremaining ring atoms are optionally and independently substituted byalkyl, aryl, aralkyl, alkylaryl, silyl, halogen, alkoxy, aryloxy,siloxy, nitro, dialkyl amino, or diaryl amino groups and two adjacentsubstituents optionally form a ring structure.
 5. The process of claim 1wherein the olefin is selected from the group consisting of ethylene,propylene, 1-butene, 1-pentene, 1-hexene, 1-octene, 4-methyl-1-pentene,and mixtures thereof.
 6. The process of claim 1 wherein the olefin is amixture of ethylene and a C₃ to C₁₀ α-olefin.
 7. The process of claim 1wherein the olefin is ethylene.
 8. The process of claim 1 wherein theactivator is selected from the group consisting of alumoxanes, alkylaluminums, alkyl aluminum halides, anionic compounds of boron oraluminum, trialkylboron and triarylboron compounds, and mixturesthereof.
 9. The process of claim 1 wherein the activator ismethylalumoxane (MAO) or polymeric MAO.
 10. The process of claim 1wherein the activator is tris-(pentafluorophenyl)borane.
 11. The processof claim 1 wherein the transition metal complex is 8-quinolinoxytitaniumtrichloride.
 12. The process of claim 1 wherein the transition metalcomplex is 8-quinolinoxytitanium tribenzyl.
 13. The process of claim 1wherein the clay is selected from the group consisting ofmontmorillonite, saponite, hectorite, mica, vermiculite, bentonite,nontronite, beidellite, volkonskoite, magadite, and kenyaite, andmixtures thereof.
 14. The process of claim 1 wherein the clay is anorganoclay.
 15. The process of claim 1 wherein the clay is heat-treatedprior to the polymerization.
 16. The process of claim 1 wherein thecomplex is supported.
 17. The process of claim 1 wherein the complex issupported on silica.
 18. A process for producing an ultra-high molecularweight polyethylene (UHMWPE), said process comprising polymerizingethylene at a temperature within the range of about 40° C. to about 110°C. in the presence of a supported Group 4 transition metal complexhaving at least one pyridine moiety-containing ligand, a clay, and anon-alumoxane activator, in the absence of aromatic solvent, α-olefincomonomer, or hydrogen, said UHMWPE having a weight average molecularweight (Mw) greater than about 3,000,000 and molecular weightdistribution (Mw/Mn) less than about 5.0.
 19. The process of claim 18wherein the non-alumoxane activator is selected from the groupconsisting of trialkyl amines, alkyl aluminums, alkyl aluminum halides,anionic compounds boron or aluminum, trialkyl boron compounds, triarylboron compounds, and mixtures thereof.
 20. The process of claim 18wherein the activator is triethyl aluminum.
 21. The process of claim 18wherein the clay is an organoclay.
 22. The process of claim 18 whereinthe transition metal complex is quinolinoxytitanium trichloride or8-quinolinoxytitanium tribenzyl.